Billions of birds are estimated to be killed striking clear and reflective windows worldwide, and conservation, ethical, and legal reasons justify preventing this unintended human-associated avian mortality. Field experiments reveal that to be effective, UV signals used to prevent bird-window collisions must minimally reflect 20–40% from 300–400 nm. Field experiments reveal 3.175 mm parachute cord hung in front of clear and reflective windows separated by 10.8 cm and 8.9 cm are effective bird-window collision preventive methods. The results of the parachute cord experiment and those of previous studies support the importance of applying collision prevention methods to the outside window surface reflecting the facing habitat and sky. Comparison of field and tunnel testing experimental protocols to evaluate bird-window collision preventive methods suggest that tunnel testing is useful for initial assessment but not as a definitive measure of effectiveness.